Cytochrome c oxidase (COX), the final enzyme of the mitochondrial respiratory chain, has a complex structure composed of 13 polypeptide subunits encoded by both mitochondrial and nuclear DNA. The three mitochondrially-encoded subunits specify the catalytic activity, while the ten nuclear-encoded subunits have unknown functions, although it has been suggested that they modulate catalytic activity of the enzyme, perhaps in a tissue-specific manner. Over the last five years, all of the nuclear-encoded COX subunits have been cloned, most by our group at Columbia, including two which have muscle-specific isoforms. We propose to use the cloned COX subunit genes (especially the two muscle-specific COX subunit cDNAs) along with subunit-specific antibodies, as probes to study the expression of these genes at the mRNA and protein levels and ultimately, to identify the genetic defect in diseases of COX deficiency. The Mendelian-inherited COX deficiency syndromes can be divided into two categories: those which are confined to only one or a few tissue types, such as the "fatal" and "benign" infantile myopathies; and those which are generalized to all tissue types such as Leigh syndrome. We now have preliminary evidence that there is a decrease in both mitochondrially- encoded and nuclear-encoded COX subunit RNA transcripts in the fatal infantile myopathy. Our preliminary analysis of Leigh patients with COX deficiency point to a defect in regulation of mitochondrial transcription. Clearly, there are interactions between the nuclear- encoded defect and mitochondrial genomes in these diseases, but these remain undefined. We also propose to study the expression of human COX subunits during normal muscle development. there are data from rat tissue that developmentally-regulated COX isozymes exist. The existence of the benign infantile COX deficient myopathy, characterized by severe muscle weakness that spontaneously improves clinically with increased expression of COX, suggests that developmentally-regulated COX subunits exists in human beings as well. We now have the COX subunit cDNAs to make probes, antibodies against COX subunits, patient material, and tissue culture systems to study COX at the molecular level in human diseases and development. I am eager to do so under the sponsorship of Dr. DiMauro and Dr. Schon, and with the collaborative assistance of Dr. Miranda for tissue culture studies, and Dr. Bonilla for histology work. My long term goal of a research-oriented career studying neuromuscular disorders.